#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<cstdio>
#include<cmath>

using namespace std;

int main()
{
	double x1, y1, x2, y2;
	cin >> x1 >> y1 >> x2 >> y2;
	printf("%.4lf", sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2)));
	return 0;
}